Filtering



Patented Jan. 25, 1938 2,106,318

UNITED STATES PATENT OFFICE FILTERING Roy D, Elliott and MaryJJ. Elliott, Jersey City,

No Drawing. Application October 15, 1932,

Serial No. 638,029

9 Claims. (Cl. 210-203) This invention relates to improvements in ing a fine turbidity. There are few turbid liqfiltering; and it comprises an improvement in uids from which clean sand grains will absorb filtering turbid liquids through pervious granucolloidally fine matter;v liquids in which these lar filter beds of inert materials wherein the matters are of such character as to tend to disgranules are provided with a coating or adsorpplace adsorbed 'water on the surface of the sand tion of an adhesive foreign material having a grains. greater physical aflinity for the particles of the Any sand filter works better after a period of turbidity than the aflinity of the untreated mause during which the pores become clogged with terial; the coating or adsorption, in the case of sediment to a certain extent; not enough to plug 10 sand filters and aqueous sugar solutions, being the filter but enough to reduce void dimensions. 10

often composed of rosin of colloidal fineness; all The sediment is then the real filtering material as more fully hereinafter set forth and as and the sand is, so to speak useful asa mechaniclaimed. cal support. In order to promote this type of In filtration of turbid liquids through pervious plugging or stoppage of the pores, in the case of granular beds, the granules are usually silica or turbid liquids carrying fine suspended matter, 15 a silicate; sand, sandlike pumicestone, asbestos, it is usual to employ "filter aids; generally kieselguhr, etc. These are the cheapest and something of the nature of paper pulp, kieselmost generally available materials. Kieselguhr guhr, etc. is composed of extremely fine particles but, for In the present invention, this defect of sand the present purposes these may be considered and silicate filters is obviatedby providing the 20 granules. Asbestos rock is sometimes used as granules with a coating or an adsorption of forgranules carrying loose surface fibers; and someeign matter having an affinity, on the one hand, times fibers are used in loose condition, functionfor sand and, on the other, for the solid particles ing in a filter in the same way as granules. For constituting the turbidity. Sometimes, this coat- 5 the purposes of the present invention, all these ing or adsorption carries an electrical charge; materials may be called sand. Unfortunately, either positive or negative, and opposite to that silica and the silicates do not have what may be of suspended colloid particles. In many cases called an attractive power or afiinity for the fine the coating or adsorption applied is of a matesolids which form the turbidity in most aqueous rial which is somewhat sticky or tacky but in liquids; wet sand neither discharges charged 001- these cases, it is not of such a character or of 30 loid particles nor tends to pick up very fine sussuch an amount to produce any tendency toward pended solids. Clean wet sand attracts and bonding the particles together. Many substances holds with great force a thin film of water are useful in the present invention, among them around it. Thus, in a filter bed composed of rosin or other resin, rubber, gum chicle, cellulose clean sand, finely divided solids may pass ennitrates, asphaltum, tar, etc. tirely through the filter bed without contacting For aqueous sugar solutions, it is found that the true surface of any granule of the filter bed. good results can generally be secured with the After a period of running, the filtering surface aid of a little rosin carried by the grains. Rosin of the sand becomes foul, first with larger paror colophony is a material of acid nature, being ticles retained by the straining action of the mainly abietic anhydrid. Ordinary rosin is not 40 bed and gradually with smaller particles of the particularly sticky or tacky at ordinary temperfilter residue. This deposit then constitutes the atures. In filtering sugar solutions, which is true filter medium and the filtrate begins to run generally done at temperatures above 60 C., bright, but by this time the rate of flow has say, about 80 C., it becomes somewhat more r at y diminished due to p l ing of the tacky, but it is not used in any amount making 45 pores. In our invention the sand grains are the grains sticky as this would interfere with the given a coating of a material having less power normal action of a granular pervious bed. A O att a film of wa e than has and, and moderate amount of colloidally fine rosin carthus suspended solids may more easily come into ried by sand grains, gives excellent results in contact with and adhere to the surface of the filtering sugar solutions, even where the b lk of 50 filter medium. Clean sand filters are most efthe suspended turbidity is of colloidal fineness. fective with fiocculated turbid liquids contain- This is particularly the case where the sugar ing coarse turbidity or sediment which can be solution has been defecated with lime and phosmechanically held in, the intergranular spaces. phate; giving precipitates of more or less basic They are of little use in clarifying liquids carrynature. 55

The for i n material may be supplied to the sand, etc., grains prior to use in filtration; or it may be supplied simultaneously; a certain amount of the foreign matter being added to; the first portion of the turbid liquid going through the filter.

In using rosin, either way is convenient. Rosin size may be diluted with water until it exhibits a faint milkiness and .this liquid poured through the filter.- The sand will pick up colloidal rosin to an extent sumcient for the present purposes. Or, if the alkalinity of the; rosin size is not unobiectionable, a little rosin size may be stirred into the first portion oi liquid to be filtered. Rosin size is rosin soap with an excess of rosin and this rosin precipitates on dilution. An alcoholic solution of rosin diluted with water is also a convenient way of producing a coating material i'or the present purposes.

For general p ses. rosin is the best adsorbing material for use with sand. It is not only adsorbed by sand, but it has adsorbing power for the usual solids or turbid aqueous solutions. But for other purposes, rubber applied in the form of latex is convenient. Commercial latex is ammoniacal and the contained rubber particles are negatively charged. It imparts a distinct tackiness to the sand grains, enabling a mechanical pick-up of solids, and it is easily applied. The same considerations apply to gum chicle. Cellulose nitrate is particularly applicable to certain types of colloid suspensions; because it has considerable adhesive power and possibly also because 'of differences in electrical charge. In all cases using stationary sand filters, it is the character of the surface at which the liquid enters which controls filtration: and in the present invention, it is sufiicient it the surface or a top layer of the filter be treated. This fact enables the extension of the present invention to certain types of granular bed devices not using silicates. The presence of adsorbed matter enhances pick-up of turbidity. Among these other types of filters are the boneblack filters used in decolorizing sugars. A boneblack filter has not only the duty of decolorizing, but, to some extent, a mechanical duty in filtration. In a columnar bone-black filter treating turbid sugar liqproviding said granules with said uors from which it is desirable to remove all haze,

it is useful to put a little colloid rosin in the top black is regenerated by heat, the rosin disappears.-

I What we claim is: e

1. In the filtration of turbid liquids through pervious filter beds oi. loose granular media, the improvement which comprises providing the granules with a light coating or adsorption of an adhesive substance having an afilnity both for the material of the granules and for the particles of the turbidity. 1

2. In the process of claim 1, the improvement which comprises providing said granules with said coating or adsorption prior to filtration.

,3. The improvement of claim 1' which comprises coating or ad sorption simultaneously with filtration.

4. The process of claim 1 wherein the granules are oi. siliceous nature.

the granules comprises passing such a turbid liquid through a pervious granular bed, the individual granules carrying a coating oi. adhesive organic material, the amount of coating and its character being such as to prevent substantial adhesion of the granules to each other.

8. In the process of claim 1, the improvement which comprises providing the granules with a coating of a tacky substance.

9. In the process of claim 1, the improvementv which comprises providing said granules with a coating of rosin, the rosin being introduced in and together with the turbid liquid.

1 ROY D. ELLIOTT. MARY J. ELLIOTT. 

